The invention relates generally to porous materials and more particularly to nanoporous fibrillar open-cellular polymer structures.
Nanoporous materials generally include a framework supporting a random structure of voids, or pores. They have many uses, for example, thermal insulation, liquid storage media and wick materials for capillary pump loop and heat pipe thermal management systems.
Capillary pump loop (CPL) and heat pipe (HP) thermal management systems use capillary action to remove heat from a source. For particular aerospace applications, CPLs and HPs need to operate over a long distance and against gravity. They have many applications, for example, as reliable cooling systems for high power density and high heat load systems such as compact directed energy weapons (DEW), air- and spacecraft avionics, radar, communications, and flight control electronics operating in high g-acceleration environments or at remote locations from the primary cooling system. In general, a CPL or HP includes a wicking structure that uses liquid coolant to move heat between an evaporator and a condenser. The ability to move coolant over long distances and against gravitational forces depends critically on the permeability and pore size properties of the wick. The highest performing wick materials are theorized to have interconnected open porosities of 90% or more and pore cell sizes less than 100 nanometers.
There is currently no satisfactory way of making high performance wick materials with both nanometer dimension pores and high porosity/permeability. Current state-of-art CPL/HP wicks have micrometer and larger size pores which significantly limit the capillary liquid pumping pressure and thus condenser-evaporator separation and the g-acceleration factor they can effectively operate under. Current wick manufacturing technology melts or fuses polymer and/or metal powders to produce monolithic tube or slab wicks. These melt/sintered wicks have pore diameters in the range of ˜5,000 to 90,000 nm (˜5 to 90 um). In addition, the pores are not regularly or uniformly distributed along the wick length. Further, the melted/sintered wicks have low porosities of the order of only 40-50%. An alternative wick structure used in CPL/HP systems is tubes with axial grooves/channels. While such wicks have higher and more uniform porosity, they have much larger capillary pores and are less able to develop high working capillary pressures.